I made this for my Neku Sakuraba cosplay outfit that I am making for the Sac-Anime. I plan to tape down my boobs when I dress in the full on costume. Sorry I didn't take pictures of my process. I got a camera just as I was finishing the project. So I tried to illustrate it as best as possible.
Get the two dark grey camis. Remove the straps and unstitch the sides. (you could simply stitch the two tops together and figure out the arm holes but it was more difficult for me.)
Stitch together the to unstitched camis lengthwise. so you have a front and back.(if you want you can zigzag stitch edges for cleaner finish)
Measure for armholes and stitch together one side avoiding armholes.
unstitch the bluish purple cami and sew sides together length wise.
Add the long bluish purple strip to the front. You can either sew the fabric on or use the stretchy fabric glue to attach like I did.
Add and sew the bias tape onto the sides of the bluish purple strip. (I thought about gluing the bias tape but it didn't look as clean because it made the tape look too dark and wet when dry.)
Sew other side of the entire piece to the other side avoiding armholes. Then sew the armholes shut by folding them over and sewing. This part is somewhat tricky. (Sewing sleeves is easier than sewing none for me >.<)
To make it easier for the cowl to stand up I folded it in half. That's optional.